1. Field of the Invention
This invention relates to printing plates used with saddles.
2. Prior Art
Printing rolls which use Linotype plates are relatively expensive, and to convert such a press to the use of inexpensive thin direct plates has heretofore involved the use of saddles which are secured to the printing rolls in lieu of the Linotype plate, the saddles themselves having a lockup mechanism for securing the relatively thin and inexpensive flexible plates thereto.
It has been known to provide holes in the ends of the printing plate to cooperate with lockup mechanism, and to further crimp such plates to assist their being held. Certain of these holes have also been used for registration purposes. Such an arrangement creates lines of weakness that tend to cause the plate to split at such holes during long press runs. With the prior art, it has been relatively difficult to automate plate manufacture in that a number of operations are required.
Further, with prior art structures, there have been loading and unloading difficulties since a press can't be reversed and only one of the plate edges is accessible. Where holes have been used, they tend to elongate during the longer press runs and thus registration control is lost.
Further, in the past, there have been undercut areas or pockets beneath the printing area to provide areas of relative weakness. If and when the paper web breaks, it tends to wrap around a roll, such condition being called in the trade a "wrap up". There might be 20 revolutions of a roll before the press is stopped, and the presence of such a quantity of paper creates a particularly large pressure under the saddle, rendering it susceptible to breakage at the points of relative weakness defined by any such pockets.
In prior manufacture referred to above, a typical first operation was to provide general forming and to include registration holes. The second operation typically included crimping of the marginal edge, and accuracy in crimping has been difficult to maintain because any inaccuracy in the crimping is reflected in loss in accuracy of registration.